I. Hutton

Thallium scans in syndrome X

Objective—To review thallium scans in patients with angina and normal coronary arteriograms. Design—Retrospective review of data. Setting—Regional cardiac centre in Glasgow. Patients—100 patients selected from those undergoing diagnostic angiography for typical angina who had normal arteriograms (around 10%), no other cardiovascular abnormality, and available thallium scans (performed routinely before angiography). Main outcome measures—Coronary arteriography, exercise tests, and gated thallium scans at peak exercise. Results—The exercise test was positive in 30 and negative in 70 patients. Thallium defects were found in 98 patients, but no consistent pattern and no significant correlation existed between the extent of thallium defect and positive exercise test or exercise tolerance. Conclusions—Thallium defects described in 98 of 100 patients with angina and normal coronary arteriograms suggest that microvascular angina may be commoner than is generally appreciated.

Quantitative gated SPECT: the effect of reconstruction filter on calculated left ventricular ejection fractions and volumes.

Gated SPECT (GSPECT) offers the possibility of obtaining additional functional information from perfusion studies, including calculation of left ventricular ejection fraction (LVEF). The calculation of LVEF relies upon the identification of the endocardial surface, which will be affected by the spatial resolution and statistical noise in the reconstructed images. The aim of this study was to compare LVEFs and ventricular volumes calculated from GSPECT using six reconstruction filters. GSPECT and radionuclide ventriculography (RNVG) were performed on 40 patients; filtered back projection was used to reconstruct the datasets with each filter. LVEFs and volumes were calculated using the Cedars-Sinai QGS package. The correlation coefficient between RNVG and GSPECT ranged from 0.81 to 0.86 with higher correlations for smoother filters. The narrowest prediction interval was 111 +/- 2%. There was a trend towards higher LVEF values with smoother filters, the ramp filter yielding LVEFs 2.55 +/- 3.10% (p < 0.001) lower than the Hann filter. There was an overall fall in ventricular volumes with smoother filters with a mean difference of 13.98 +/- 10.15 ml (p < 0.001) in EDV between the Butterworth-0.5 and Butterworth-0.3 filters. In conclusion, smoother reconstruction filters lead to lower volumes and higher ejection fractions with the QGS algorithm, with the Butterworth-0.4 filter giving the highest correlation with LVEFs from RNVG. Even if the optimal filter is chosen the uncertainty in the measured ejection fractions is still too great to be clinically acceptable.

Quantitative gated SPECT myocardial perfusion imaging with 201Tl: an assessment of the limitations

Gated SPECT (GSPECT) perfusion imaging has been increasing in popularity both with 99Tcm agents and 201Tl. However, both higher activities than administered in the UK and multi-headed cameras are often used. The aim of this study was to assess GSPECT imaging using lower activities of 201Tl with a single-headed camera. Seventy patients underwent stress and redistribution GSPECT imaging after a mean injected activity of 62±7 MBq 201Tl. These patients also underwent radionuclide ventriculography (RNVG) imaging. The Cedars Sinai Quantitative Gated SPECT (QGS) package was used to calculate left ventricular ejection fraction (LVEF) from the GSPECT studies. Comparison of ejection fractions calculated using GSPECT with those calculated using RNVG yielded a correlation coefficient of 0.70 for the stress studies and 0.71 for the redistribution studies. The width of the mean 95% prediction interval ranged from 22 to 74 percentage points for the stress studies and 22 to 86 percentage points for the redistribution studies. Ejection fractions calculated from stress and redistribution GSPECT studies showed a correlation of 0.80 with a mean 95% prediction interval of 42.6±0.4 percentage points. In conclusion, left ventricular ejection fractions calculated using the QGS algorithm from 201Tl GSPECT studies are inadequate for use in clinical practice.

The detection of coronary artery disease: A comparison of exercise thallium imaging and exercise equilibrium radionuclide ventriculography

This study compared the accuracy of rest and exercise gated equilibrium technetium ventriculography with exercise thallium imaging in 50 consecutive male patients undergoing routine coronary angiography for the evaluation of chest pain. No patients were excluded on the basis of prior myocardial infarction, nature of angiographically defined coronary disease or symptoms. Antianginal therapy was continued in all patients. Eight patients had normal coronary arteries, 9 had single vessel, disease, 20 had double vessel disease and 13 had triple vessel disease. Sixteen patients had previously documented myocardial infarction. Using exercise radionuclide ventriculography, 34 patients with coronary disease were detected resulting in a sensitivity of 81%; 6 patients with normal coronary arteries had normal scans, a specificity of 75%, with a predictive accuracy of 80%. In comparison, thallium imaging detected 42 patients with coronary disease resulting in a sensitivity of 100%. Six patients with normal coronary arteries had normal thallium images resulting in a specificity of 75% and a predictive accuracy of 96%. These results suggest that exercise thallium imaging is a more accurate investigation than exercise equilibrium radio-nuclide ventriculography and is the investigation of choice in the noninvasive detection of coronary artey disease.

A comparison of maximal exercise and dipyridamole thallium-201 planar gated scintigraphy

Both symptom-limited maximal exercise and intravenously given dipyridamole stress (0.56 mg/kg over 4 min with a 2 min walk) gated thallium scans were performed in 22 patients undergoing coronary arteriography for the assessment of chest pain. All scans were acquired gated to the electrocardiogram in 3 projections and were reported for the presence and extent of defects in 5 myocardial segments in each view. In addition, left and right ventricular myocardial uptake and estimates of right and left lung and liver to left ventricular uptake were assessed relative to the injected dose of thallium-201. Overall, 190/310 segments were abnormal with exercise compared with 169/310 with dipyridamole. Segments were scored greater in extent in 90/310 cases with exercise, compared with 46/310 in which the defect was more extensive with dipyridamole (P <0.0005). Non-attenuation corrected percentage myocardial thallium uptakes were similar for both stresses: anterior percentage uptakes, 0.785%±0.230% with exercise versus 0.870%±0.217% with dipyridamole (NSD). Left and right lung and liver to left ventricle ratios were all significantly higher with dipyridamole than with exercise (1.587±0.408 versus 1.446±0.518, P <0.02; 1.78±0.479 versus 1.46±0.502, P <0.002; 2.598±0.788 versus 1.265 ± 0.386, P < 0.001, respectively). High right and left lung uptakes with dipyridarnole were strongly correlated with high exercise values (r =0.756, P <0.001; r =0.809, P < 0.001). The liver uptake was weakly correlated between the 2 different stress tests (r =0.483, P < 0.02). These results demonstrate that dipyridamole, at 0.56 mg/kg over 4 min, induces fewer and less extensive thallium perfusion defects than maximal exercise, and that liver and lung to myocardial ratios are higher with dipyridamole than with exercise.

Are ejection fractions from gated SPECT perfusion studies clinically useful? A comparison with radionuclide ventriculography

Gated SPECT (GSPECT) was evaluated for the measurement of left ventricular ejection fraction (LVEF) by comparing with equilibrium gated radionuclide ventriculography (RNVG). A total of 99 subjects underwent GSPECT and RNVG imaging. All studies were acquired in list mode with GSPECT studies processed to give 16- and 8-frames per R-R interval, and RNVG studies 24 frames per R-R interval. The Cedars-Sinai QGS software was used to calculate ejection fraction from GSPECT studies. RNVG studies were processed using a manually drawn single region of interest technique. Comparison of LVEF from GSPECT with RNVG yielded correlation coefficients of 0.82 and 0.81 for 16- and 8-frame GSPECT studies respectively. The mean 95% prediction interval was 33 +/- 11 percentage points for both 16- and 8-frame studies, indicating a great disparity between predicted ejection fraction values from GSPECT and actual RNVG values. Subgroup analysis of 29 patients with pathological Q-wave evidence of myocardial infarction demonstrated a poorer correlation coefficient of r = 0.69. Subgroup analysis of 32 patients with end-diastolic volumes < 100 ml demonstrated a poorer correlation coefficient of r = 0.32. Ejection fractions calculated from 16- and 8-frame studies showed a correlation of 0.99 with a mean 95% prediction interval of 8.7 +/- 0.04 percentage points. The 8-frame studies underestimated LVEF by 3.6 +/- 2.3% compared to the 16-frame studies. In conclusion, left ventricular ejection fractions calculated using the QGS algorithm from GSPECT studies are inadequate for use in clinical practice.

Improved detection of coronary artery disease by estimated myocardial thallium uptake.

Myocardial thallium uptake has been assessed at the time of thallium scanning in a group of 50 male patients undeergoing coronary arteriography and 10 young healthy volunteers. The net thallium dose injected was obtained by counting the dose prior to injection using the gamma camera and counting the syringe and IV cannula after injection. Significantly higher levels of myocardial thallium uptake were obtained in both the volunteers and patients with normal coronary anatomy (1.36%±0.32%, n=10 and 0.93%±0.26%, n=9, respectively) compared to patients with single, double or triple vessel coronary artery disease (0.63%±0.19%, n=11; 0.70%±0.20%, n=15; 0.67±0.18, n=15, respectively). Exercise tests were positive in 46% of patients with coronary artery disease with an overall predictive accuracy of 56%. Thallium scans were positive in 68% of patients at a specificity of 89%. If the range of myocardial thallium uptake from the patients with normal coronary arteries is used to define a lower limit of normal, then the sensitivity of the thallium scan with thallium uptake is 90% with a predictive accuracy of 90% in the detection of significant coronary artery disease in this group of patients. Thus, estimation of total % thallium uptake is a simple index which yields useful diagnostic clinical information.

Exercise 201Tl/rest 99Tcm-tetrofosmin myocardial perfusion imaging : A convenient protocol for the assessment of coronary disease

Standard exercise thallium-201 (201Tl)-redistribution protocols for the detection of coronary artery disease take about 4 h to complete. This is inconvenient for both patients and staff. The higher energy technetium-99m (99Tcm) emissions permit immediate imaging after 201Tl with minimal crosstalk. This study assessed exercise gated planar 201Tl scintigraphy (55 MBq) followed by rest gated planar 99Tcm-tetrofosmin scintigraphy (250 MBq) in 32 patients. The results showed a high sensitivity for the detection of coronary disease (100%) in this highly selective group of patients. In order to diagnose myocardial infarction accurately, it was necessary to view the gated 201Tl images and assess regional wall motion in a defect zone. This gave a specificity of 88% and a sensitivity of 71% for the prediction of myocardial infarction on the angiographic ventriculogram. Stress 201Tl/rest 99Tcm-tetrofosmin is a useful short protocol for patients unable to complete the full 4-h exercise 201Tl-redistribution study.

Rest or redistribution thallium myocardial imaging for resting myocardial perfusion : A detailed comparison with regional wall motion

Redistribution thallium-201 (201T1) imaging is the most common method of assessing resting myocardial perfusion. However, the equivalence of a redistribution image and a separate rest injection is unclear. Although the presence of a defect on rest imaging has normally been equated with the presence of a myocardial infarction, it has recently been shown that a significant proportion of fixed defects on exercise-redistribution 201T1 actually represent areas of viable myocardium. This study was a detailed comparison of rest and redistribution imaging in 30 patients undergoing routine exercise 201T1 scanning for the assessment of coronary artery disease. A small dose (15 MBq) of 201T1 was administered at rest following the imaging in three standard planar views. Similar stress images were acquired using a further 50-55 MBq of 201T1 administered at peak effort. Redistribution images were acquired 3-4 h later and equilibrium blood pool ventriculography performed using in vivo labelling with 600 MBq 99Tcm-pertechnetate. Of 150 abnormal segments on the exercise scans, 74 (49%) were identified as being reversible on the redistribution scans and 58 (39%) on the rest images. Only 39 (53%) of these reversible defects were identified on both the redistribution and rest scans. Only 41% of the fixed defects on the redistribution images (32% of fixed defects on the rest images) had abnormal wall motion. Therefore, rest and redistribution images are not equivalent. Both rest and redistribution images significantly overestimate myocardial infarction. This may have significant effects on patient selection for revascularization procedures and therefore all patients having perfusion scintigraphy should also have additional assessment of regional wall motion to allow accurate classification of the functional status of myocardial segments.

A comparison of adenosine and exercise stress 201T1 scintigraphy.

A detailed comparison of stress thallium images utilizing exercise (symptom-limited bicycle ergonometer) and adenosine (infused at 50 μg kg-1 min-1 increasing by 25 μg kg-1 min-1 every 2 min to a maximum tolerated dose) was performed in 20 patients with angiographically documented coronary disease. Ten patients were receiving beta-blockade at the time of both tests. Triple-, double- and single-vessel disease was present in eight, seven and five patients, respectively. Exercise produced a large increase in double product (8970 ± 288 to 20 984 ± 690 mm Hg min-1) while adenosine produced no significant change (8440 ± 280 to 9086 ± 600 mm Hg min-1). Each of the three gated planar images (anterior 40° and 70° left anterior oblique) was divided into five equal segments. Exercise produced 44/90, 44/95 and 45/95 abnormal segments in the anterior, 40° and 70° views while adenosine produced 53/100, 44/100 and 52/100 abnormal segments for the same views. The total number of abnormal segments was similar in both groups (133/280 exercise and 149/300 adenosine). Each abnormal segment was analysed for degree of change between stresses using a five-point scoring system. Exercise produced eight segments which were larger by one point and 44 segments larger by two points while adenosine produced 17 and 44 segments larger by one and two points respectively. Left ventricular uptake (as % injected dose) was significantly greater in the adenosine group (1.12 ± 0.06% versus 0.64 ± 0.05%, P<0.01) but right ventricular uptake was similar (0.15 ± 0.1% versus 0.14 ± 0.09%). In summary adenosine does produce thallium defects comparable to exercise. Despite no significant change in double product with adenosine, thallium defects were of similar size and distribution to those produced by exercise. Beta-blocker therapy had no significant effect on thallium defects.